The present invention is directed to the area of cellular cushioning articles, such as BUBBLE WRAP® cellular cushioning, and processes for making same, in which first and second multilayer films are joined together to form fluid-filled cells therebetween. More particularly, the present invention is directed to improved cellular cushioning articles, and to processes for making such improved articles.
Cellular cushioning material is used to package items, e.g., by wrapping the items in the cushioning material and placing the wrapped items in a shipping carton, or simply placing one or more cushions inside of a shipping carton along with an item to be shipped. Alternatively, the cushioning material may form the inside of a ‘padded mailer,’ which is a flexible mailing envelope to which a cushioning material is internally adhered, and in which an object to be mailed may be placed and sealed prior to deposit with a courier. In all of the foregoing applications, the cushioning material protects the packaged item by absorbing impacts that may otherwise be fully transmitted to the packaged item during transit, and also by restricting movement of the packaged item within the carton.
Commercial BUBBLE WRAP® brand cellular cushioning material utilizes two films that are laminated together. A first type of such cellular cushioning articles has a first film that is embossed, i.e., thermoformed in a manner to provide a plurality of protrusions when viewed from an outer side of the thermoformed film, the protrusions being pockets or cavities when viewed from an inner side of the thermoformed film. The protrusions may have a cylindrical (or hemispherical) shape, i.e., with a round “footprint”, cylindrical, conic section, or hemispherical walls, and a flat top, domed top, or point top. The transition between the walls and the top can be provided with a radius. The inner surface of the unformed area (i.e., herein referred to as the “land area”) of the thermoformed film is laminated to a second film that is a non-thermoformed, flat film, resulting in the encapsulation of a fluid (i.e., broadly including gas and/or liquid; preferably air) within each of the resulting fluid-filled cells. Each fluid-filled cell comprises the fluid encapsulated between a protrusion in the thermoformed film and a portion of the flat film that corresponds with the footprint of the protrusion. This first type of cellular cushioning is recognized as being of the “single cell” type.
A second type of cellular cushioning comprises a first film that is thermoformed with the plurality of protrusions as described above, with at least a portion of the land area of the first film thereafter being laminated to at least a portion of a land area of a second film that has also been thermoformed in a manner that results in a plurality of protrusions. The resulting cellular cushioning article is recognized as being of the “double cell” type.
In both the single-cell type cellular cushioning and double-cell type of cellular cushioning, each fluid-filled cell comprises the fluid therein plus the surrounding portion of the first and second films that are in contact with the fluid. When in use, any elastic and/or inelastic compressibility provided by the fluid in the fluid-filled cells, together with any elastic and/or inelastic extension of the surrounding film portions, can contribute to the cushioning function while the cell is under load.
Conventional methods of making cellular cushioning materials, such as BUBBLE WRAP® brand cellular cushioning, use a vacuum source to deform a heated polymer film to thermoform pockets that can be filled with fluid, e.g., air or other gas, and then sealed to a second film to produce fluid-filled cells. Such products can be made using a temperature-controlled drum having recesses connected to a vacuum source. When vacuum is applied to a heated film in contact with the drum, the regions of the film suspended over the drum recesses are drawn into the recesses. The film may be heated by the drum and/or may be heated prior to contact with the drum, e.g., due to recent emergence from an extrusion system. In either case, the film is maintained at a temperature to provide it with sufficient pliability to be drawn into the drum recesses, and also to bond to the second film. Those regions of the heated film which are drawn into the recesses are deformed and thinned by the vacuum drawing process. One side of the resulting thermoformed film offers a flat surface for lamination thereto, i.e., has a flat land area with spaced concavities from the forming process, while the other side does not offer a flat surface for lamination, but rather has formed protrusions thereon with a flat land area at the base of the protrusions, but which is unavailable for lamination due to the protrusions extending from the land area. A second film, which generally is a flat film, i.e., not thermoformed, is fused to the “flat side” of the formed film, more specifically to the land area portion of the formed film, resulting in a plurality of sealed, air-filled cells. The fusion of the first and second films generally occurs via heat-sealing.
Conventional cellular cushioning fabricating processes may also include as a first stage, a film extrusion step; as second stage, a film thermoforming step; and as a third stage, a film lamination step, with the stages being carried out in a single, integrated process, as disclosed in U.S. Pat. Nos. 3,294,387 and 6,800,162, both of which are hereby incorporated herein, in their entireties, by reference thereto. In the first stage, polymer films are extruded by conventional techniques known to those in the art of polymer film fabrication. In the second stage, one or both of the films are thermoformed by the vacuum forming technique described above, and two films are combined in the third stage to formed sealed, air-filled cells, according to heat sealing methods that are known to those in the art of polymer film sealing.
While BUBBLE WRAP® cushioning material has been made and used in a commercially-successful manner for a number of years, there remains a need for improvement. Specifically, there is a need to reduce the amount of polymer used to make the films from which the material is formed, while maintaining in such material sufficient cushioning performance to protect objects packaged in the material. Such a reduction in polymer usage would beneficially reduce the utilization of petroleum and natural gas resources, from which most of the polymers employed in cushioning materials are derived.
One way to reduce the amount of polymer used in one or both of the films is to improve the strength obtained from a film of a specified thickness. Providing a stronger film made from any given amount and type of polymer would allow the film to be downgauged while maintaining or improving the performance of the resulting cellular cushioning article.
Another way to reduce polymer usage is to substitute recycled polymer(s) for one or more “virgin” polymers (i.e., new or unused polymer), in the material with recycled polymer. However, as the use of recycled polymer in films has the potential to result in a degradation of the properties of such films and, thereby degrade the performance of cushioning materials made from such films, it would be desirable to enhance the relative amount of recycled polymer in the films without adversely affecting the performance of the resulting cushioning article.
Accordingly, a need exists in the art to reduce polymer usage in films from which the cushioning articles are made, both by producing a mil-for-mil stronger film using the same or similar polymers that have been used to make prior art cellular cushioning articles, as well as including recycled polymer in cellular cushioning materials in such a way that virgin polymer usage is reduced and cushioning properties are maintained or improved.